1. Field of the Invention
The present invention relates to an improved structure of a desktop scanning device, and particularly, to an improved platform arrangement which can prevent the occurrence of a darkened image generated by a gap existing between an upper cover and a transparent plate located on the scanning device during the scanning process.
2. Description of the Prior Art
Referring to FIG. 1, it is a side view of a platform arrangement of a traditional flatbed scanner which illustrates an upper housing 10, a transparent plate 20, a calibration strip 30, an upper cover 40 and a background plate 50 (usually in white color). The calibration strip 30 is installed between the upper housing 10 and the transparent plate 20 shown in FIG. 1. The way the calibration strip 30 is installed will probably give rise to drawbacks as stated below.
First of all, during the assembly of the scanner, the white surface of the calibration strip 30 performed as the calibration parameter may be stained in some way, such as operator's fingerprints. The calibration performance may thus be reduced. The stained calibration strip 30 may not be easily removed and replaced by a clean one once the calibration strip 30, the upper housing 10 and the transparent plate 20 are bonded by glue, unless they are disassembled, respectively. However, the transparent plate 20 or the upper housing 10 may be spoiled during the disassembly.
Furthermore, the upper cover 40 of the flatbed scanner is usually equipped with a background plate 50 for providing a background color of the object to be scanned. Preferably, when the upper cover 40 is pulled down over the transparent plate 20 to start the scanning process, the transparent plate 20 can be completely covered by the background plate 50 without leaving any gap, so that a most complete background color can be provided without affecting the scanning performance. Nonetheless, owning that the upper cover 40 is a movable element, in actual operation of the flatbed scanner, a gap D (when the transparent plate 20 is not totally covered by the background plate 50, the gap D is a gap in width, while when the transparent plate 20 is totally covered by the background plate 50, i.e. the front end of the background plate 50 exceeds the point F, the gap D is a gap in height due to a bevel G shown in FIG. 1) may probably be created, and a darkened image data may be generated when the sensor (not shown) of the flatbed scanner detects the existence of the gap D during scanning process. The scanning performance may this be reduced. As illustrated in FIG. 2, if the gap D does exist, a darkened image 200 may be generated at both sides of the image 100 after the object is scanned.